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Exit pupil & common bino sizes?

I'm looking for some binoculars to use deer stalking and most the common sizes seem to be 8x42, 10x42 etc. (Maybe this is just in my price range? < £300).

The exit pupil on these are circa 4-5mm. I read the pupil dilates to 7mm on average so why isn't a 6x42 a more common size?

I'd prefer smaller binos but wonder if I should be looking at something like an 8x56?

Also... would a pair of 8x42 Leica/Swarovski be "brighter"/clearer than a pair of cheaper 8x56? I.e. A more expensive binocular with a smaller exit pupil than a cheaper binocular with a larger exit pupil?

Ah ok thanks FGYT, I thought it may be a bit bigger than so that's good! I guess the 7mm figure is for complete darkness so maybe 5mm would be closer for dusk also. Good point MarkFox, didn't think about that!

Steiner does a 7x50 which is a good compromise. They are branded 'Marine Navigator' but there is no reason why you shouldn't use them for stalking. You'll find quite a few brands offer different liners for different markets (hunting, birdwatching, marine..) but the technical spec is often the same. Marketing..

Funny things bino's, I have had 10x32's, 8x42's 8x32's plus an old pair of naval 8x60's all have their plus points.
A few years ago I bought a pair of Zeiss 8x20 Victory's as a pair to keep in my pocket while fishing etc.
Then started using them for shooting, now they are my only bins, do everything I need with a great picture and
work surprisingly well at last light. I'm not saying I'd use them for first and last light deer stalking, but I would certainly
trust them to do the job once the sun is up.

They are branded 'Marine Navigator' but there is no reason why you shouldn't use them for stalking.

Most binos that are for marine use are autofocus (read: no focus!). They have adjustment in both eyes but no central focus. You should adjust them once for your eyes and leave at that, no problem if you're using them at hundreds of meters.

It's different when you're looking at, say 20-200 meters. I find this type hard to use since your eyes are doing all the work. It gets worse in the dusk.

That said, most autofocus, especially porro prism type, are better quality, more robust and more water resistant for the same money.

The exit pupil on these are circa 4-5mm. I read the pupil dilates to 7mm on average so why isn't a 6x42 a more common size?

'Cos it's like the number of cupholders in a car. The bigger the number the better people think it is for them and the more want to buy it. Sort of "Well if I can see Y well at 6x then I'll see Z even better if I buy 8x or 10x".

Military binoculars OTOH tend to be set to a magnification that works and gives a greater depth of focus and, as importantly width of view. After all it's not a probem if you miss a deer or can't see the colour of the crest on a lesser spotted oak warbler but it is if men's lives depend on the matter.

So 6x and 7x used to be the classic military magnifications. Regardless of the overall size of the binoculars. Indeed my late father's military binoculars...for artillery spotting...still somwhere in the house I think...were 7x50 with military graticules on the lenses.

My own choice is a pair of Leica BA 7x42 and a pair of Optolyth 7x50 as if you need more then take a telescope! Having said that the best greater magnificaion binoculars I had were a set of the last Schott glass Zeiss 10x42 and they were superb.